The cornea was dissected under the microscope to its three layers. The in vitro behavior of isolated epithelium, stroma or endothelium as well as the reciprocal influence of these layers in combined cultures was studied. Electron microscopic and metabolic studies of epithelia or stromal cultures, on the one hand, and of combined cultures, on the other hand, demonstrated that keratocyte activity was inhibitied by the presence of epithelial cells in culture. Endothelial membranes consisting of Descemet's membrane and cultured endothelial cells were kept in culture for up to eight weeks and transplanted in vitro onto corneas devoid of Descemet's membrane. Most endothelial membranes retained their characteristics after transplantation.